Something's totally borked. Try a fresh install of a different distro
KDE
KDE is an international technology team creating user-friendly free and open source software for desktop and portable computing. KDE’s software runs on GNU/Linux, BSD and other operating systems, including Windows.
Plasma 6 Bugs
If you encounter a bug, proceed to https://bugs.kde.org/, check whether it has been reported.
If it hasn't, report it yourself.
PLEASE THINK CAREFULLY BEFORE POSTING HERE.
Developers do not look for reports on social media, so they will not see it and all it does is clutter up the feed.
Similar experience sometimes with snaps. Some snaps take way too long to open. I have taken to just manually installing .Deb files for applications, but I will just ship and switch to Debian next.
This shouldn't happen. Try a different Distro
5 seconds to open anything
Define anything. The Firefox snap is not a speed demon, Steam is not one either. Have you actually tried gaming? Have you looked at KSysGuard, Top or any other performance monitor app to see if you have any CPU/memory hogs around?